case re-sizing

hi all.
im new to re-loading.
my choosen method of re-sizing cases is to bump the cases back .001 with the full length die.
iv started with factory hornady ammo, after firing the ammo, using the hornady headspace gauge iv ended up with 2.1225. all cases are even. (this is 7mm rem mag)
so cool, i bumped them back to 2.1215.
while setting up the die some cases bumped a bit far, so to make those cases all even and to be kept seperate, i full length sized them down to the shell holder, giving me a measurment of 2.1115

so now i figure, i will just develop two loads at the same time, one with my bumped cases at 2.1215 the other with full length sized cases at 2.1115, no drama.

i run my bumped cases through a ladder test going up .5 grains until max.
cool now i have a max to not go past, and an idea of velocity. plus a rough idea where a accuracy node maybe. i use the remaining cases to do a few three shot groups to find a good group and a low ES. i also used my few full length sized cases to do some groups. (being that the F/L cases and the bumped cases will give me different results from the different size cases)

meanwhile i also full length sized some cases from another barrel, but they gave me another measurment of about 2.1130 which i couldnt really understand. (slightly longer, even though i screwed the die past the shell holder a bit)

anyway the bumped cases (most of them) that have been fired or grouped didnt expand properly and seemed to have got slightly shorter with the headspace gauge
by maybe .0005

what im trying to do is not full length size but to just bump back .001
but i now have a heap of cases that are a bit short to get my original bump of 2.1215.
so i can only really full length size them. but im trying not to work the brass that much.

im using 2217 or h1000 the book max is 68.3. and the max i found was 73.5, but at 73 the shot had a wierd sound, so iv called that my max. 73.5 had extractor marks on the case head 73 did not.

so i dont really understand why my cases arnt expanding properly, and i have a heap of brass all at different lengths.
some are a bit short of my bump to length, very little have expanded to my chamber size and iv ended up with two lots of full length sized cases with different lenghts. (all lengths i speak of are with the hornady head space gauge)

how do others keep there cases the same, to in-sure an accurate load.
is there anything that sticks out that im doing wrong? even my three shot groups of 71.8, 72, 72.2 didnt expand properly. but the factory superformance ammo had no problem, and it starts at 2.0970 the shortest of all. the one case of 73.5gr that has pressure signs on the case head is the only one that actually grew in headspace length.
hopfully, this is understandable, any tips would be great.
thanks.

You're not thinking about what you're doing.
You said to begin that you wanted to bump cases 1thou. Well you're not suppose to bump from just any ole number, but from chamber fit. And you can't do this until your actually get there(fully fireformed).
When you sized them all from 2.1225 to 2.1115, you departed from your goal of 1thou straight to 11thou! You're also straying from "trying not to work the brass that much" which is causing a mess & it will only get worse pretty fast.

You're not thinking about what you're doing.
You said to begin that you wanted to bump cases 1thou. Well you're not suppose to bump from just any ole number, but from chamber fit. And you can't do this until your actually get there(fully fireformed).
When you sized them all from 2.1225 to 2.1115, you departed from your goal of 1thou straight to 11thou! You're also straying from "trying not to work the brass that much" which is causing a mess & it will only get worse pretty fast.

the factory ammo i fired all measured a consistant 2.1225. so while this might not be fully expanded to the chamber, i figured its a good place to bump them from, and back .001, rather than full length size them back .011 (why go all that way back if i dont need to)

the few that i did size to 2.1115. were not the bulk of the cases, they were a few that went past 2.1215 when i was setting up the die , so they became full length sized to keep them all the same. and were used for fouling only.

the full length sized cases (about 5) grew after firing from 2.1115 to 2.1200 consistantly.

the cases i bumped to 2.1215 ended up from .0005 to .0200 smaller. they were different charges so i dont mind them being in-consistant. but however they didnt expand to my starting size, or even grow past it. except one case which had pressure signs on the case head.

so now my theory is. the factory superformance ammo, must have quite some pressure behind it, and the rounds i loaded didnt have as much, except the one with pressure signs.
so i should have just started by full length sizing everything, even though i have a reliable chamber sized piece of brass to bump back from.

You're not thinking about what you're doing.
You said to begin that you wanted to bump cases 1thou. Well you're not suppose to bump from just any ole number, but from chamber fit. And you can't do this until your actually get there(fully fireformed).
When you sized them all from 2.1225 to 2.1115, you departed from your goal of 1thou straight to 11thou! You're also straying from "trying not to work the brass that much" which is causing a mess & it will only get worse pretty fast.

+1

Only bump brass if chambering becomes difficult.

Factory brass is always smaller so it will fit in any chamber. Some manufacturers under size even
more than the SAMME spec. for use in semi autos and full autos.

Size brass only as needed and no more, and brass will last a lot longer. For gas guns full length
sizing is recomended to improve function.

If you are going to "bump" the shoulder start with fire formed brass and measure the chamber,
then bump your .0005.

If this is a bolt gun I would recomend only neck sizing till bolt lift gets tight. I have some hornady brass for my 243 that shot 32 times before needing a bump. Your gun will tell you when to bump!
I would fl size the cases you bumped and re-fire form